1. Field of the Invention
This invention relates to apparatus for the forging of metals, in particular to apparatus known as forging machines.
2. Description of the Prior Art
Forging machines, that is to say rapid stroke forging presses with two rams or at the most four rams which in this case lie in an x-shaped arrangement in one plane, are offset by 90.degree. relative to one another and act radially on the workpiece, are designed with mechanical or hydraulic ram drives and are used for reshaping workpieces extended on their longitudinal axes. Mechanical ram drives permit very high working speeds and stroke rates of the rams, but the depth of penetration is small. If greater depths of penetration are required, hydraulic ram drive is advantageous. In the ram motion, a distinction is to be made between the working stroke proper, and the part of the stroke in which the measure of the ram approach, i.e., the workpiece dimensions, is preset. This measure, or the position in which the working stroke is effected, is designated the stroke position, which is adjusted by stroke position adjustment. Stroke position adjustment by changing the amount of liquid in the cylinders which are provided for the full range of the stroke is precluded, in the case of rapid stroke forging presses, because of the high level of cushioning action due to the presence, in most stroke positions, of an unnecessarily large volume of pressurized fluid. For a long time, therefore, the drive for the stroke position adjustment has been separated from the hydraulic drive for the working stroke. In this case, the pistons which move the rams have been disposed in short-stroke cylinders of small volume specified by the piston stroke and the piston surface, and the piston stroke is mechanically limited by stops, while the stroke position adjustment is generally carried out mechanically separately by spindles. Thus it is known (German published specification OS 21 43668) to provide an annular piston for the working stroke, which is non-rotatably guided in a cylinder and is provided with a threaded bore, in which a threaded spindle is rotatably inserted, which acts on the ram. The guidance play can be kept to a minimum by direct guiding of the ram in the machine frame, however it is disadvantageous for several, e.g. four, annular pistons to be symmetrically connected to each ram with an inserted threaded spindle, as this requires considerable structural expenditure. A less expensive solution (Peter Metzger, "Die numerisch gesteuerte Radial-Umformmaschine und ihr Einsatz im Rahmen einer flexiblen Fertigung" - "The numerically controlled radial forming machine and its use in the context of flexible manufacture" - Volume 55 of the reports from the Institut Fur Formtechnik of the University of Stuttgart, ed Prof Dr-Ing K Lange, Springer-Verlag, Berlin- Heidelberg-New York, 1980, pages 38, 112, 113) is to move the cylinders with the pistons and rams, for the purpose of stroke position adjustment, via spindles, mounted on the cylinders, by means of worm wheels, worms and servomotors, which requires particular guiding means for the adjustable cylinders. The guiding of the ram in the cylinder and the cylinder in the machine frame inevitably leads to higher guide play of the ram with respect to the machine frame